Hyperaromatic Stabilization of Arenium Ions: Acid-Catalyzed Dehydration of 2-Substituted 1,2-Dihydro-1-naphthols
作者:Jaya Satyanarayana Kudavalli、Dara Coyne、Rory A. More O’Ferrall
DOI:10.1021/jo2020483
日期:2012.1.6
correlation is taken to indicate that cis substuents are reacting normally, differentiated only by their inductive effects. The slower reactions of the trans isomers are the judged to be “abnormal”. This is confirmed by comparing effects of cis and trans β-OH substituents on the reactivities of dihydro phenols, naphthols, and phenanthrols. Whereas kH/kOH for cis substituents varies by less than 8-fold
对于酸催化脱水速率常数顺-2-取代的1,2-二氢萘由塔夫脱关系日志良好相关ķ = -0.49 - 8.8σ我,与OH和OME轻微负偏差。相比之下,反式取代基与σI的相关性较弱,并且在大多数情况下,其反应比顺式异构体慢。该行为与速率确定的2-取代碳阳离子(萘离子)中间体的形成一致,该中间体对顺式反应物具有2-CH键,其取向适合与电荷中心超共轭。对于反式异构体2-取代基本身在阳离子的最初形成的构型中定向为超共轭。有人认为,ķ顺/ ķ反式率比率的取代基(ME,8.4;卜吨,12.7; pH值,3.8; NH 3 +,160; OH,440)反映他们hyperconjugating能力相对于氢。对于已知的(RS,N 3)或怀疑的(EtSO,EtSO 2)通过π或σ邻基效应稳定阳离子的取代基,观察到反式异构体的反应更快。Taft相关性好表明顺式学生的反应正常,仅因其感应作用而有所区别。反式异构体的较